|  | 1.4 | Network Layer Functions
| 1.4.2 | Network and subnetwork addresses in the IP
In a TCP/IP environment, end stations communicate with servers, hosts, or other end stations. This occurs because each node using the TCP/IP protocol suite has a unique 32-bit logical address, known as the IP address. In addition, within a TCP/IP environment, each network is seen as a single unique address. That address must be reached before an individual host within that network can be contacted. Networks can be segmented into a series of smaller networks called subnetworks. Thus, an IP address is broken up into the network number, the subnetwork number, and the host number. Subnets use unique 32-bit subnet addresses that are created by borrowing bits from the host field. Subnet addresses are visible to other devices on the same network, but they are not visible to outside networks. Subnetworks are not visible to outside networks because the outside networks can only reference the subnet's whole network address. With subnets, network address use is more efficient. There is no change to how the outside world sees the network, but within the organization, there is additional structure. In Figure network 172.16.0.0 is subdivided into four subnets: 172.16.1.0, 172.16.2.0, 172.16.3.0, and 172.16.4.0.
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| Subnetting